Coating apparatus with improved doctor means



- y 1965 I J. A. VAZDIKIS 3,182,632

COATING APPARATUS WITH IMPROVED DOCTOR MEANS Filed Feb. 5, 1962 2 Sheets-Sheet 1 INVENTOR J'ANIS ALFRED VAZDIKIS ATTOR NEYS J. A. VAZ'DIKIS 3,182,632.

2 Sheets-Sheet 2 "May 11, 1965 I COATING APPARATUS WITH IMPROVED DOCTOR MEANS Filed Feb. 5, 1962 FIG. 4

United States Patent Filed Feb. 5, 1962, set. No. 171,105 4 Claims. c1. 11s- 1o4 The present invention relates to apparatus of the type used for coating rapidly moving webs of material by an application of more than sufficient amounts of coating composition thereto and the subsequent removal of excess amounts to reduce the finished coating to the desired predetermined thickness. More particularly, the invention relates to a novel and improved doctor means for producing extremely uniform, smooth and defect-free web coatings while operating at. economically high rates of speed.

Specifically, the presentinvention finds great utility in machines for coating traveling webs of fibrous material such as paper wherein the maintenance of a high quality coating, of uniform thickness and free of streaks, scratches and other defects, hasbeen extremely difiicult, if not virtually impossible, at high rates of speed owing to the tendency of the doctor surfaces to'become fouled by particles of foreign matter unavoidably present in the coating composition.

Various methods and apparatus have been employed in an attempt to maintain the working edge of the doctor means in an effectively uniform condition, free from dust particles and other foreign matter, but none has proven to be nearly as effective as desired for continual high speed operation. The criticality of. maintaining the working edge of the doctor in a uniform condition and free of foreign matter is, of course, well understood in the .coating art. The resultant uniformity of surface finish and the uniformity of coating thickness are directly contingent upon the uniformity of the working edge and its freedom from accumulations of foreign matter. Thus, when the'working edge of the doctor means accumulates foreign material, as is not unusual in conventional coaters, the web coating will become streaked and scratched, and the quality of the output willbe greatly reduced. i

The machine of the present invention essentially comprises a resilient support for a traveling web, means for applying an excess of coating composition to the traveling web, and novel and improved doctor means for spreading and metering the coating material onto the traveling web in a thin, even, andsmooth finished coat, substantially free of streaks, scratches and other undesirable coating defects.

A significant feature of the invention resides in the provision of improved doctor means, which includes a work- 3,182,632 Patented May 11, 1965 ice With the wire continually moving across the surface of the Web, the working edge of the doctor (the wire itself) is constantly kept clean by continuous wiping as it leaves engagement with the surface of the web. Hence, a doctor with a clean, uniform working edge, free from accumulations of foreign particles, is constantly drawn across the web surface, and uniformity and high quality of coating finish is thus insured. With the new apparatus, accumulations of foreign matter that would otherwise cause a shutdown, or certainly reduce the quality of performance of a conventional coating machine are quickly carried away its engagement with the traveling web. during the coating operation, to produce extremely uniform and smooth web coatings while operating at high rates of speed. By providing a moving doctor of adequate length to permit constant wiping of temporarily inactive portions thereof,

a uniform, clean working edge, free of accumulated foring edge in thesirnple but etficient form of a filament such tration but not limitation will be referred to hereinafter as a wire, is pressed against the surface of the traveling web and iscontinually moved across the surface of the web by a cooperating driving means. The wire may be supported by means which advantageously cause or permit controlled rotation of the wire about its own axis while the wire itself moves transversely of the traveling web. The wire, the length of which is advantageously at least twice the width of the web, is guided by suitable means in its traverse-of the web, the guide means advantageously being designed to" accommodate sensitive adjustment of the nip across the web.

yieidable contact with the web. ,This arrangement per-f mits a sensitivenip adjustment across the web. 7

The endless wire, which moves transversely relative to the web, advantageously may be given a simultaneous rotational movement relative to its own axis or, alternatively, the wire may be rotated from time to time. to bring new surface portionsthereof into operative position. This arrangement maintains the working edge ofthe doctor (the wire itself) in a substantially uniform condition and significantly prolongs its useful life. During a coating operation, an independent wiping means, proximately disposed to a side of the web, continuously scrapes any accumulation of foreign matter from the wire as it leaves the web. The combination of the wiping operation away' from the web surface and the transverse relative motion of the working edge of the doctor means with the traveling Web enables high quality, high speedcoating to be simply, economically, and reliably performed. I

An alternative embodiment of the invention employs a wireof finite length supported by a frame mounted on a coating machine for reciprocal movement relative to the traveling web, provision advantageously being made for intermittently rotating the wire to increase its life. In the alternative embodiment, cleaning or wiping means are disposed on both sides of the traveling Web to permit the wire to be wiped along its entire active length during each complete reciprocal stroke of the wire across the Web. A resiliently mounted wire guide means similar in construction-and function to that of the first preferred embodiment is also provided.

In the preferred embodiments of this invention, a moving-elastic bed is provided for web support. The elastic bed maycomprise a resilientback-up roll located im mediately adjacent the doctor means for advantageous use with a web of low strength, while an alternative ar rangement comprises a moving belt to offer a blanket type of support for the Web and to reduce the tension therein. The latter form of elastic moving bed is advantageous for use in the coating of a web of very low tensile strength. In lieu of using a single back-up roll or spaced rolls, another preferred arrangement utilizes a pair of rolls in spaced relation to the moving doctor to provide support while coating a web of sufficient strength and resiliency to effectively serve as its own elastic bed.

In the foregoing preferred embodiments of the invention, impressions of varying designs may be imparted to the traveling web by substituting a suitably engraved wire for the plain wire.

For a more complete understanding of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a longitudinal cross-sectional view of an improved web coating apparatus incorporating the principles of the invention;

FIG. 2 is a plan view of the coating apparatus of FIG. 1;

FIG. 3 is a plan view fa modified form of coating apparatus according to the invention;

FIG. 4 is a schematic representation of a continuous belt web supporting means for use in conjunction with the coating apparatus of the invention; and

FIG. 5 is a schematic representation of spaced roll web supporting means for use in conjunction with the coating apparatus of the invention.

A coating machine constituting a first preferred embodiment of the invention, illustrated in FIGS. 1 and 2 of the drawings, comprises a driven roll for conveying a web of material 11 (typically paper) continuously past a coating station, indicated generally at 12. The roll 10 is advantageously provided with a resilient outer covering 13 and thus forms a moving elastic bed to support the web 11 as it passes the coating station 12.

In the illustrated form of the invention, the web, supplied from a suitable source, engages the bottom of the supporting roll 10 and travels upwardly, around a portion of the roll, and leaves the roll after passing the coating station 12. Before reaching the coating station, the outer or exposed surface of the web has applied thereto a layer of coating composition which is slightly greater than the desired coat weight. The initial coating may be applied by any suitable means and, for purposes of illustration only, the applicator is shown to comprise a roller 15,which is partially immersed in a bath 14 of coating material and is driven to rotate synchronously with the linear movement of the paper web 11. The coating material is picked up by the surface of the roller 15 and transferred to the surface of the web, as the web travels past the roller in contact with the upper surface thereof.

In accordance with the invention, the coating station 12 comprises a doctor in the form of an endless wire 16 supported by sheaves 17 and 18 which are mounted, respectively, on shafts 19 and 20. The wire 16, which is advantageously about /8 inch in diameter, is guided across the traveling web surface 110, in yieldable contact therewith, by means of a longitudinal wire guide 21, and is driven continuously across the web by the sheave 18 which in turn is driven by appropriate extrinsic drive means 1811.

In the illustrated form of coating apparatus, the respective shafts 19, 20 are mounted in a suitable supporting frame comprising a tubular crossbeam 24 disposed transversely of the web 11. Advantageously, the shaft 20 is mounted in fixed relation to the crossbeam 24 while the shaft 19 is adjustably mounted by a slide block 22, guided by tracks 23 for movement toward and away from the shaft 20. Adjustment of the tension in the wire 16 is achieved by movement of the slide block 22 in its guide tracks 23 upon actuation of an adjusting screw 25 attached to the slide 22 and threaded into a removable end 4; plate 26, the latter being secured to the crossbeam 24 by conventional screws 26a.

A wire guide 21 provides for uniform pressure of the wire 16 against the traveling web 11 and advantageously offers additional support for the wire 16. The wire guide 21 advantageously is formed of such material, and in such configuration, as to be of a semi-resilient nature. In addition, the wire guide is adjustably and resiliently supported at a plurality of spaced points along its length, so that the pressure of the wire 16 against the web may be carefully adjusted and maintained in a susbtantially uniform condition.

In the illustrated apparatus, the wire guide 21 is supported in cantilever fashion by a plurality of threaded rods 27, which are slidably received in tubular bushings 27a extending transversely through the tubular crossbeam 24. At each side of the crossbeam 24, each of the threaded rods 27 receives an adjusting assembly comprising a compression spring 28, positioned between a pair of washers 29, and an adjusting nut 30. Thus, each of the threaded supporting rods 27 may be adjusted independently, toward or away from the backing roll 10, by appropriate manipulation of the adjusting nuts 30, the supporting rods 27 being guided by set screws 31 for movement along their axes without rotation.

Normally, the supporting rods 27 are brought into proper initial adjustment, in setting up the equipment, and are not further adjusted, except as may be required from time to time to maintain uniformity of wire pressure across the full width of the web.

Sensitive adjustment of the pressure between the wire 16 and the web 11 advantageously is achieved by pivoting the crossbeam 24 through supporting legs 33 about the axis of a cross shaft 34 upon which the legs 33 are mounted. The cross shaft 34 is supported for rotation by spaced journal housings 35 mounted on the coating machine frame 36. Controlled pivoting of the entire wire supporting structure is effected by movement of pivot arms 37, fixed in depending relation to the cross shaft 34 and engaged at one side by adjusting screws 38. The adjusting screws 38 are opposed by spring means 39 held in compression between arm surfaces 37a and the coating machine frame 36. Sensitive adjustment of the wire 16 against the web 11 is accomplished by manipulation of the adjusting screws 38, the arrangement being such that, as the screws are backed off, the wire 16 is urged toward the web surface by the springs 39. In this respect, it will be understood that the effective strength of the springs 39 is such that, if the screws 38 were completely backed off, causing the wire 16 to be brought to bear against the web under the full pressure of the springs 39, the wire pressure against the web would be greater than that necessary or desired for effective doctoring action.

A pair of oppositely rotating, angularly disposed rearrangement wheels 41 and 42 is provided to engage opposite sides of the wire 16 moving transversely of the web 11 and to thereby impart rotary motion to the moving wire 16 about its own longitudinal axis. The rotation of the wire 16 tends to even out Wear of the wire, greatly prolonging its useful life. Furthermore, the combination of the relative motion of the web and the rotary motion of the transversely moving wire results in an effectively helical motion of the wire. This helical motion has been found to be desirable in obtaining extremely uniform, coated surfaces free of streaks, scratches, and other defects at high rates of speed.

In the illustrated form of the invention, an independent wiper 43 is advantageously positioned at the side of the web 11. This arrangement effectively accommodates remote wiping of the doctor and thus constantly cleans the doctor of foreign particles and removes the particles from the system. In this respect, the use, as a doctor, of a wire that is constantly moved beyond the web surface, permits the doctor to be continuously cleaned and inspected remotely of the web, during the coating operation,

without necessitating a shutdown of the coating machine.

An alternate preferred embodiment of the present invention, shown in FIG. 3 of the drawings, comprises a driven roll 110 for conveying a web (not illustrated) of material continuously past a coating station indicated generally at 112. The roll 110 is advantageously provided with a resilient outer covering 113 and thus forms a moving elastic bed to support a web as it passes the coating station 112.

In this particular embodiment,-as in the first preferred embodiment of the invention, an excess of coating composition is applied to the web in a suitable manner. The applicator roll and the bath of coating composition 14 (FIG. 1) are illustrative of an arrangement suitable for this purpose.

In accordance with the alternative embodiment of the invention, the coating station 112 comprises a 'doctor in the form of a finite wire 116 tautly supported by clamping devices 117 and 118, which are mounted by spaced legs 122 and 123 of a U-shaped tension frame 124. The clamping devices 117 and 118 advantageously can be intermittently rotated to prolong the useful life of the wire 116. The wire tension frame 124 is reciprocated in a track 125 of a coating machine body 126 by appropriate extrinsic drive means, such as indicated at 126a, to move the wire 116 continually, back and forth, across the traveling web surface. Thus the wire 116, about /s inch in diameter, or of smaller or larger diameter, is reciprocated continually within tension frame 124 across a traveling web surface while being maintained in a substantially fixed, yet slightly yieldable contact therewith by means of a longitudinal wire guide 121. The length of the wire 116 is advantageously about twice the width of the web, permitting the entire working edge of the doctor (wire 116) to be cleaned once each reciprocal stroke.

The wire guide 121, which may be identical in construction to the wire guide 21 shown in FIGS. 1 and 2 and described in detail above, is adjustably and resiliently supported at a plurality of spaced points along its length so that the pressure of the wire 116 against the web may be carefully adjusted and maintained in a substantially uniform state.

In the apparatus shown in FIG. 3 the wire guide 121 is supported in cantilever fashion by a plurality of threaded rods 127, slidably received in openings 127a extending transversely through a cross bar 120, which is advantageously a part of the coating machine body 125. At each side of the cross bar 121), each of the threaded rods 127 receives an adjusting assembly comprising a compression spring 128, positioned between washers 129 and an adjusting nut 130. Thus each of the rods 127 may be adjusted independently toward or away from the backing roll 110 by appropriate manipulation of the adjusting nuts 130, the rods 127 being guided by set screws 131 for movement along their axes without rotation.

As explained in connection with the apparatus of FIGS. 1 and 2, the rods 127 ordinarily are initially adjusted during the set up of the equipment and are not further adjusted, except as may be required from time to time to maintain uniformity of wire pressure across the full width of the web. I

Independent wipers 143 and 144 are located on both sides of the web. As in the first preferred embodiment, the wiper arrangement insures that foreign matter and excess coating composition will be removed from the wire at points effectively remote from the web. It is the constant reciprocating movement of inactive portions of the wire to a location beyond the web surface that permits the wire to be cleaned away from the web while the coating operation is continued by active portions of the wire. It will be apparent from the foregoing description that, by using a wire of sufficient length (advantageously at least twice the width of the web) and reciprocating the tension frame 124 in strokes about equal to or greater than the width of the web, the entire doctor surface (wire 6 116) can be continually cleaned without interrupting the coating operation.

FIGS. 4 and 5 show schematically two arrangements, in addition to use of the back up roll (16 in FIG. 1; in FIG. 3), for use in either preferred embodiment of the invention, for supporting the traveling Web as it passes the coating station. In the coating of webs having'high tensile strengths, the web itself can serve as the elastic movable bed; hence, support by spaced rolls 50 and 51 (FIG. 5) is sufficient. However, if the web is fragile and does not possessadequate tensile strength, a continuous moving belt 52 (FIG. 4) may be provided to give the proper support, as the web passes the coating station.

A deflector plate 32, best seen in FIGS. 4 and 5, may advantageously be attached by suitable means to the wire guide 21 to divert excess coating composition from the moving wire 16 to the bath of coating material 14 for subsequent use.

The new coating means, while being of relativelysnnplified and economical'construction, enables significant advantages to be realized in the coating of webs. Spe cifically, the provision of a doctor element, in the form of an elongated wire, permits continuous cleaning of the doctor during the progress of a coating operation, such that foreign particles are continually removed from the system. The invention is especially advantageous in connection with the coating of papers, since the occurrence of common coating defects, such as streaks and scratches, is significantly reduced by the prompt elimination of foreign particles. In this respect, the coating of papers using blade-type coaters, is sought to be carried out at very high Web speeds, and the continued presence of foreign particles about the working edge of the doctor can result in the scrapping of substantial footage due to defects, which give the coated web poor printability, or otherwise render it less suitable or unsuitable for its intended purpose.

Although the present invention has been described with reference to specific, preferred embodiments, it should be understood that the disclosure has been made only by way of example and that certain changes in details of construction and in the combination and arrangement of parts may be made without departing from the spirit and scope of the invention as hereinafter claimed.

I claim:

1. Apparatus for coating a traveling web comprising (a) a coating station,

(b) means for conveying a web continuously past said coating station and web supporting means engaging the back surface of the web in the region of said coating station and providing continuous support for said traveling web,

(0) means for applying a coating composition to the outer surface of said traveling Web,

(d) said coating station being provided with a doctor means positioned to bear against the outer surface of said traveling web in the region of said web supporting means to meter and smooth the coating cornposition on said web, I

(e) said doctor means comprising an endless cylindrical flexible wire element forming a doctorin-g edge,

(f) said flexible wire element being disposed generally transversely of said traveling Web and engaging said web across its full width,

(g) said flexible wire element having an effective length not substantially less than twice the width of said traveling web,

(11) means for controllably tensioning said wire and for moving said flexible wire element continually along its longitudinal axis and across the surface of said travel ing, coated web,

(5) means for guiding said flexible wire element in its transverse movements and for supporting said flexible wire element in predetermined pressure engagement with said surface of said traveling web,

(j) means for cleaning said flexible wire element of coating composition cooperating with and movable relative to said flexible wire element, and

(k) at least two wheels rotating in opposite directions, said Wheels engaging opposite sides of the moving flexible Wire element to impart rotary movement thereto about its own longitudinal axis.

2. A coater according to claim 1 in which said means for moving said flexible wire element continually along its axis and across the surface of said traveling coated web comprises a plurality of rotatable sheaves.

3. A coater according to claim 2 in which at least one of said sheaves is adapted for movement relative to the other to accommodate adjustment of the tension in the moving flexible wire element mounted thereon.

4. A coater according to claim 2 in which said sheaves and said means for guiding said flexible wire element are supported by a rigid structural element disposed transversely of the traveling web, said element being movable relative to said Web for adjusting the predetermined pressure engagement of said flexible wire element with the surface of said traveling web.

References Cited by the Examiner 5 UNITED STATES PATENTS 1,043,021 /12 Mayer 118120 X 2,148,456 2/39 Grossarth 101-169 2,271,458 1/42 Lionne. 2,508,287 5/50 Outterson et al 117102 X 19 2,534,320 12/50 Taylor 117-111 X 2,598,733 6/52 Warner. 2,664,792 1/ 54 Cook. 2,695,004 11/54 Montgomery et al. 118-104 X 2,807,891 10/ 57 Roscoe. 15 3,048,874 8/62 MacDonald 15256.51

FOREIGN PATENTS 1,094,628 12/54 France.

RICHARD D. NEVIUS, Primary Examiner. 

1. APPARATUS FOR COATING A TRAVELING WEB COMPRISING (A) A COATING STATION, (B) MEANS FOR CONVEYING A WEB CONTINUOUSLY PAST SAID COATING STATION AND WEB SUPPORTING MEANS ENGAGING THE BACK SURFACE OF THE WEB IN THE REGION OF SAID COATING STATION AND PROVIDING CONTINUOUS SUPPORT FOR SAID TRAVELING WEB, (C) MEANS FOR APPLYING A COATING COMPOSITION TO THE OUTER SURFACE OF SAID TRAVELING WEB, (D) SAID COATING STATION BEING PROVIDED WITH A DOCTOR MEANS POSITIONED TO BEAR AGAINST THE OUTER SURFACE OF SAID TRAVELING WEB IN THE REGION OF SAID WEB SUPPORTING MEANS TO METER AND SMOOTH THE COATING COMPOSITION ON SAID WEB, (E) SAID DOCTOR MEANS COMPRISING AN ENDLESS CYLINDRICAL FLEXIBLE WIRE ELEMENT FORMING A DOCTORING EDGE, (F) SAID FLEXIBLE WIRE ELEMENT BEING DISPOSED GENERALLY TRANSVERSELY OF SAID TRAVELING WEB AND ENGAGING SAID WEB ACROSS ITS FULL WIDTH, (G) SAID FLEXIBLE WIRE ELEMENT HAVING AN EFFECTIVE LENGTH NOT SUBSTANTIALLY LESS THAN TWICE THE WIDTH OF SAID TRAVELING WEB, (H) MEANS FOR CONTROLLABLY TENSIONING SAID WIRE AND FOR MOVING SAID FLEXIBLE WIRE ELEMENT CONTINUALLY ALONG ITS LONGITUDINAL AXIS AND ACROSS THE SURFACE OF SAID TRAVELING, COATED WEB, (I) MEANS FOR GUIDING SAID FLEXIBLE WIRE ELMENT IN ITS TRANSVERSE MOVEMENTS AND FOR SUPPORTING SAID FLEXIBLE WIRE ELEMENT IN PREDETERMINED PRESSURE ENGAGEMENT WITH SAID SURFACE OF SAID TRAVELING WEB, (J) MEANS FOR CLEANING SAID FLEXIBLE WIRE ELEMENT OF COATING COMPOSITION COOPERATING WITH AND MOVABLE RELATIVE TO SAID FLEXIBLE WIRE ELEMENT, AND (K) AT LEAST TWO WHEELS ROTATING IN OPPOSITE DIRECTIONS, SAID WHEELS ENGAGING OPPOSITE SIDES OF THE MOVING FLEXIBLE WIRE ELEMENT TO IMPART ROTARY MOVEMENT THERETO ABOUT ITS OWN LONGITUDINAL AXIS. 